Field
The disclosed embodiments relate to batteries for portable electronic devices. More specifically, the disclosed embodiments relate to techniques for performing multi-phase charging of batteries with boost bypass.
Related Art
A portable electronic device is typically configured to shut down when its battery reaches a predetermined minimum voltage, which may be higher than the lowest operating voltage of the battery. For example, although a lithium-ion battery may be considered empty when the battery voltage reaches 3.0V, certain components of the computing device (e.g., the radio and speaker subsystems of a mobile phone or tablet computer) may require a minimum voltage of 3.4V to operate, and the device may be configured to shut down at 3.4V to avoid browning out these components. As a result, the battery may contain unused capacity between 3.0V and 3.4V.
The amount of unused capacity may depend on the load current, temperature and age of the battery. For light loads on warm, fresh batteries, the unused capacity is typically just a few percent of the overall capacity. For colder or older batteries, however, the unused capacity may increase dramatically. For example, FIG. 1 shows an example of batteries discharged at a given load (0.5C load, which is the current required to discharge a battery in two hours) at two different temperatures. As shown there, discharging the battery at 25° C. may result in a few percentage of the overall capacity occurring under a cutoff voltage (shown in FIG. 1 as 3.4V), but discharging the battery at 0° C. may result in as much as 30% of the overall capacity occurring under the cutoff voltage. Accordingly, it may be desirable to have a system that is able to take advantage of this unused capacity.